Improve javadoc for when to use class names rather than class references #48395
Description
See spring-projects/spring-framework#35959 for background.
We can improve our class-level Javadoc to indicate when a .class reference can be used and when a String name should be used.
Annotations we might want to consider include @AutoConfigureAfter, @AutoConfigureBefore and @AutoConfiguration.
@ConditionalOnClass has some Javadoc that we could use as a template.